1. Field of the Invention
The present invention relates to a high-pressure fuel supply pump for supplying fuel to the fuel injector of a cylinder injection engine.
2. Description of the Related Art
FIG. 5 is a sectional view showing a conventional high-pressure fuel supply pump. A high-pressure fuel supply pump 1 shown in FIG. 5 is mounted on a housing or the like of an engine, which is not shown; it is driven via a cam 39 which rotates at half the rotation speed of the engine. Formed in a casing 48 of the high-pressure fuel supply pump 1 are an intake passage 36, a discharge passage 37, and a return passage 26. Further, a cylindrical cavity 48a is formed at the bottom of FIG. 5.
A sleeve 70 having a cylinder section 70a is provided in the cavity 48a, the sleeve 70 being disposed with one end thereof oriented toward a bottom section 48b of the cavity 48a. The sleeve 70 is composed of the cylinder section 70a, a thick-wall section 70b formed by increasing the wall thickness of one end of the bottom section 48b of the cylinder section 70a, and a fixing section 70c shaped into a flange on the end of the thick-wall section 70b, the end being the one closer to the bottom section 48b.
Provided between the bottom section 48b and the sleeve 70 are a first plate 45, a second plate 47, and a lead valve 46 clamped therebetween. The first plate 45 and the second plate 47 have an intake port communicated with the intake passage 36, a discharge port communicated with the discharge passage 37, and a return port. The lead valve 46 is provided with an intake valve and a discharge valve which are located at the positions matched to the intake port and the discharge port, respectively, and which allow fuel to pass only in one direction, and a return port.
In the cylinder section 70a of the sleeve 70, a substantially cylindrical piston 53 is provided so that it may reciprocate. The piston 53 and the cylinder 70a together constitute a fuel pressurizing chamber 52. A compression coil spring 55 is held in a compressed state in the fuel pressurizing chamber 52, the compression coil spring 55 being positioned by a spring holder 54.
Provided around the sleeve 70 is a housing 44 which surrounds the sleeve 70. The housing 44 is shaped like a substantially bottomless bowl; it has a cylindrical edge section 44a on the outer periphery thereof. A holder 42 is secured to the end of the piston 53 on the opposite side from the fuel pressurizing chamber 52. A metallic bellows 43 is provided between the housing 44 and the holder 42; the bellows 43 holds therein the fuel which has leaked through between the piston 53 and the sleeve 70.
A bottomed cylindrical tappet 56 serving as a driver is held against the end of the piston 53 on the opposite side from the fuel pressurizing chamber 52; the tappet 56 has a cam roller 59, which is rotatably supported by a pin 57, therein. The cam roller 59 is abutted against the cam surface of a cam 39. A spring holder 60 is secured to the tappet 56, and a compression coil spring 61 is provided in a compressed state between the spring holder 60 and the housing 44.
Provided around the compression coil spring 61 is a bracket 58 for securing the high-pressure fuel supply pump 1 to the housing or the like of an engine, which is not shown. The bracket 58 has a substantially cylindrical shape and it has a flanged section 58a in the middle thereof, the flanged section 58a having a plurality of through holes 49 at predetermined points around the circumference thereof. The casing 48 has tapped holes 50 at the positions matched to the through holes 49. Bolts 51 are inserted in the through holes 49 to be tightened into the tapped holes 50. This tightly secures the bracket 58 to the casing 48. The high-pressure fuel supply pump 1 is fixed to the housing or the like of the engine, not shown, by the outer peripheral section of the bracket 58 thereof being supported.
One end section 58c of the bracket 58 pushes an edge section 44a of the housing 44 to push the fixing section 70c of the sleeve 70 against the casing 48 via the edge section 44a. This fastens the sleeve 70 to the casing 48. The fixing section 70c must be securely fastened to ensure good sealing relative to the plate 47 and to prevent fuel leakage through the lead valve 46. A predetermined gap is formed between the rear surface of the flanged section 58a and the casing 48 so as to permit the fixing section 70c to be firmly pushed.
A tappet sliding surface 58b is formed on the inner side of the opening end of the bracket 58 on the opposite side from the flanged section 58a. The tappet sliding surface 58b supports the tappet 56 so that it may reciprocate.
Formed in the casing 48 are a fuel inlet 18a communicated with the intake passage 36 and afuel discharge port 18b communicated with the discharge passage 37. The fuel inlet 18a is provided with a filter 19. A piston damper 21 is provided in the middle of the intake passage 36. A buffer vessel 23 and a resonator 24 are provided in the middle of the discharge passage 37; the buffer vessel 23 and the resonator 24 are communicated with a communicating passage 25. A return passage 26 returns the fuel accumulated in the bellows 43 to a fuel tank, which is not shown. Connected to the casing 48 is a return pipe 27 that is connected to the return passage 26. Further, a return pipe 28 is connected to a piston damper 21.
In the high-pressure fuel supply pump thus constructed, the piston 53 is pressed against the tappet 56 by the compression coil spring 55, the tappet 56 being pressed by the compression coil spring 61 so that it is held always in contact with the cam 39. The rotation of the cam 39 causes the piston 53 to reciprocate in the cylinder section 70a.
When the piston 53 comes down, the fuel flows from the intake passage 36 and passes through the lead valve 46 into the fuel pressurizing chamber 52. When the piston 53 goes up, the intake valve of the lead valve 46 closes, while the discharge valve opens to let the fuel in the fuel pressurizing chamber 52 to be discharged through the discharge passage 37. The fuel leaked from between the piston 53 and the sleeve 70 is accumulated in the bellows 43 and returned to the fuel tank, not shown, through the return passage 26.
In the high-pressure fuel supply pump having the constitution described above, the sleeve 70 is secured to the casing 48 by being fastened by the bracket 58. When fixing the sleeve 70, however, the fixing section 70c is subjected to the compressing force acting in the axial direction of the cylinder section 70a, thus deforming the inner surface of the cylinder section 70a.
FIG. 6 is a sectional view showing the shape of the conventional sleeve 70 when it has been deformed. The arrows in the drawing indicate the directions of the forces applied when the sleeve 70 is secured to the casing 48; the solid lines show the configuration before the sleeve 70 is fastened to the casing 48, the dashed lines show the deformation after the fastening, and the chain line indicates the highest position of the stroke of the piston 53.
The sleeve 70 is secured to the casing 48 by the fixing section 70c which is firmly fastened in the vertical direction in FIG. 6. At this time, the deformation that takes place in the fixing section 70c is transmitted to the sleeve 70, causing the inner surface of the cylinder section 70a as indicated by the dashed lines. There has been a problem in that the deformation adversely affects the reciprocating motion of the piston 53 and causes the projecting section of the inner surface of the cylinder 70a to wear abnormally with consequent seizure.
Further, the predetermined gap is formed between the rear surface of the flanged section 58a and the casing 48, whereas the fastening bolts 51 are disposed at the predetermined positions in the circumferential direction; therefore, firmly fastening the bracket 58 onto the casing 48 undesirably causes the flanged section 58a to develop wavy deformation in the circumferential direction. This leads to uneven circumferential force pressing the fixing section 70c of the sleeve 70, and the sleeve 70 deforms also in the circumferential direction. As a result, the reciprocating motion of the piston 53 is further affected and the sealing performance is deteriorated with consequent deterioration in the performance of the pump.
In addition, the deformation of the bracket 58 also adversely affects the reciprocating motion of the tappet 56, deteriorating the slidability of the tappet 56.